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Questions and Answers about Combat Robotics
from Team Run Amok


Radio Reception Problems in Combat Robots
 
Combat robots are electrically very 'noisy'. Electronic speed controllers, relays, and motors all contribute to electrical noise in radio frequencies that makes the control signal from your transmitter difficult to receive. The problem is particularly acute in larger robots with higher-power components, and in larger arenas where the distance to the robot is greater.

Steps you can take to avoid/cure reception problems:

  • Avoid AM radios – Inexpensive Amplitude Modulation (AM) radios are allowed in many events for robots up to 12 pounds without active weapons, but they are particularly sensitive to interference from robot components. Use a coded Frequency Modulation (FM) 75 MHz or digital 900 MHz or 2.4 GHz system for best reception.

  • Read the radio manual – Modern 'spread spectrum' 2.4 GHz receivers may have multiple short antennas, or even multiple receiver modules. Pay attention to the manufacturer's instructions on the orientation of the antennas/modules.

  • Expose the antenna – Plastic armor is transparent to radio waves, but metal or carbon armor blocks reception. Get your antenna out of the box!

  • Do not shorten/lengthen antenna wires – The length of an antenna wire is critical for best reception. 75 MHz FM receiver antennas are quite long -- you may be able to wind most of the wire around a plastic drinking straw with just the last few inches exposed. Experiment.

  • Keep antenna away from metal – Put some space between your antenna and your armor. Don’t lay an antenna flat against a metal or carbon fiber plate.

  • Do not point the transmitter antenna at the robot – The strongest signal comes from the sides of the transmitter antenna, not the tip. Keep the transmitter antenna vertical.

  • Put suppression capacitors across motor brushes – Motor brushes create electrical noise. A ceramic capacitor (0.1uF) across the positive and negative motor leads as close to the brushes as possible will reduce this noise. Additional capacitors from each lead to the motor case my help, or may actually hurt. Experiment as required.

  • Keep power wires short – Power wires to motors, speed controllers, and batteries can act like transmitter antennas to broadcast the electrical noise sources. Keep them short, and twist the positive and negative leads around each other about every six inches.

  • Isolate the receiver – Put the receiver as far from interference as possible, away from speed controllers and motors. A metal box around the receiver itself may help in difficult circumstances -- but run the antenna outside the box.

  • If all else fails... – Try a separate battery pack for the receiver rather than pulling receiver power from the speed controller or from the main battery pack. The main battery may drop voltage under load and cause the receiver to lose the signal, or the power line may carry an interference signal directly.



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Copyright 2012 by Mark Joerger -- all rights reserved.